Method for the preparation of styrene polymer foam and foam prepared thereby

ABSTRACT

Mechanically stable styrene polymer foams having highly desirable physical properties are prepared employing as a blowing agent a mixture of lower alcohols with chlorofluoromethanes.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 426,414, filed Sept. 29,1982.

One of the larger applications for styrene polymer foams is in the fieldof thermal insulation. The styrene polymer foam suitable for thermalinsulation desirably has relatively small cells and dimensionalstability. It is also desirable that the insulating value of the foam bemaintained for as long a period as possible. The variety of styrenepolymer foams contemplated within the scope of this invention are theso-called extruded foams. Such extruded foams have a fairly uniform cellsize when compared to the so-called molded bead foams. Extruded foamsare also employed in the so-called decorative field wherein a foam plankmay be cut into a decorative foam and be used as is or used as a basefor further decorative material. Particularly desirable stable styrenepolymer foam is obtained employing the method set forth in U.S. Pat. No.3,960,792 to M. Nakamura. For a considerable period of time, styrenepolymer foams have been extruded employing methyl chloride alone as theblowing agent or a mixture of methyl chloride with chlorofluorocarbons.When employing such a system in extrusion, generally the foam must beaged for a period of time to permit the methyl chloride to leave thecells and air to enter by an appropriate diffusion process through thecell walls. Also, in foams employing methyl chloride as the totalblowing agent or as a partial blowing agent, the period of aging forthicker extruded boards and planks can present an inconvenientwarehousing problem. Also, due to the undesirable physicalcharacteristics of methyl chloride, caution and good ventilation areutilized when such foams are cut to shape.

Extruded foams and their manufacture are discussed in great length inU.S. Pat. Nos. 2,409,910; 2,515,250; 2,669,751; 2,848,428; 2,928,130;3,121,130; 3,121,911, 3,770,688; 3,815,674; 3,960,792; 3,966,381;4,085,073 and 4,146,563, the teachings of which are herein incorporatedwith reference thereto.

It would be desirable if there are available an improved process for thepreparation of alkenyl aromatic polymer foam.

It would also be desirable if there were available an improved processfor the preparation of an alkenyl aromatic polymer foam which did notemploy methyl chloride as the blowing agent.

It would also be desirable to replace methyl chloride with a relativelynon-toxic readily available material.

These benefits and other advantages in accordance with the presentinvention are achieved in a process for the preparation of an alkenylaromatic thermoplastic resinous elongate foam body having a machinedirection and a transverse direction, the body defining a plurality ofclosed noninterconnecting gas-containing cells therein, the steps of themethod comprising heat plastifying an alkenyl aromatic syntheticresinous material, adding to the heat plastifying synthetic resinousmaterial a volatile fluid foaming agent to provide a foaming agentresinous polymer mixture under a pressure sufficiently high that foamingis prevented, mixing the fluid foaming agent with the plastified resinto form a blowable resinous mixture, reducing the temperature of themixture to a temperature such that when pressure is removed therefrom, afoam of desirable quality is obtained, reducing the pressure on themixture to thereby cause the mixture to form a foam of desired quality,the improvement which comprises employing a blowing agent selected fromthe group consisting of

(1) a blowing agent mixture of from about 5 to 20 weight percentisopropyl alcohol, from about 5 to 50 percent chlorodifluoromethane, andfrom about 30 to 70 percent dichlorodifluoromethane;

(2) a mixture of from about 5 to 50 percent of an ethanol, methanol ormixtures thereof, from about 5 to 50 percent of chlorodifluoromethane,and about 30 to 70 percent dichlorodifluoromethane;

and mixtures thereof, all percentages being by weight.

Also contemplated within the scope of the present invention is asynthetic resinuous thermoplastic foam prepared in accordance with thehereinbefore described method wherein an alkenyl aromatic thermoplasticsynthetic resinous elongate foam body having a machine direction and atransverse direction, the body defining a plurality of closednoninterconnecting gas-containing cells therein, the cells having anaverage cell size of from about 0.1 to 1.2 millimeters and preferablyfrom about 0.1 to 0.9 millimeters, the foam body being of a generallyuniform cellular structure and being without discontinuities, the bodybeing without substantial variation in average cell size when cell sizeis measured by averaging cell diameter across the minimumcross-sectional dimension of the body (i.e., such as by ASTM MethodD2842-69), the elongate body having a cross-sectional area of at least 8square inches and having a minimum cross-sectional dimension of at least0.25 inch, the foam body having a water vapor permeability not greaterthan 1.8 perm inches as measured by ASTM Method C355-64 Procedures forDesiccant method, a density of from about 1 to about 5 pounds per cubicfoot with the further limitation that the cells contain a blowing agentwhich has a permeability through the alkenyl aromatic resinous polymerof not greater than 0.017 times the permeability of nitrogen through thebody a C₁ to C₃ monohydric alcohol and the blowing agent having athermal conductivity not greater than 0.08 British thermal units-inchper hour per square foot per degree Fahrenheit.

By the term "alkenyl aromatic synthetic resin" is meant a solid polymerof one or more polymerizable alkenyl aromatic compounds. The polymer orcopolymer comprises in chemically combined form, at least 70 percent byweight of at least one alkenyl aromatic compound having the generalformula ##STR1## wherein Ar represents an aromatic hydrocarbon radical,or an aromatic halo-hydrocarbon radical of the benzene series, and R ishydrogen or a methyl radical. Examples of such alkenyl aromatic resinsare the solid homopolymer of styrene, a-methylstyrene, o-methylstyrene,m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylxylene,ar-chlorostyrene or ar-bromostyrene; the solid copolymers of two or moreof such alkenyl aromatic compounds with minor amounts of other readilypolymerizable olefinic compounds such as methylmethacrylate,acrylonitrile, maleic anhydride, citraconic anhydride, itaconicanhydride, acrylic acid, rubber reinforced (either natural or synthetic)styrene polymers, etc.

Blowing agents useful in the practice of the present invention may be ofcommercial purity and generally are satisfactory. However, denaturedethyl alcohol is available in a wide variety of formulations whereindenaturing is accomplished by adding materials ranging from methanol tolow volatility materials such as hard soap, sulfuric acid and the like.In order to be suitable for the practice of the present invention, suchdenatured alcohol should in general be noncorrosive to the processingequipment or to the environment in which the foam so prepared is to beused. Furthermore, in order to provide a desirable foam, a denaturedethanol should not unduly depress the heat distortion temperature. Inorder to determine whether a particular denatured alcohol is suitablefor the practice of the present invention, one percent by weight of thealcohol based on the weight of the polymer is incorporated in thedesired polymer, the resultant mixture injection molded. The injectionmolded test piece is maintained under pressure until it has solidifiedto thereby prevent foaming of the test piece. The Vicat heat distortiontemperature of the molded specimen is then determined in accordance withthe American Society for Testing Materials Test D-1525-76. A similarinjection molding is made employing polymer without the denaturedalcohol and the Vicat heat distortion determined in a similar manner. Ifthe heat distortion temperature of the sample containing 1 percent ofthe denatured alcohol is not more than 7 degrees centigrade below theheat distortion temperature of the sample without alcohol, the alcoholis satisfactory for the practice of the present invention. However, ifthe heat distortion temperature of the sample containing the alcoholbeing evaluated is more than about 7 degrees centigrade below that ofthe sample molded without the denatured alcohol, the alcohol isunsatisfactory for the practice of the present invention. Typicalsuitable denatured alcohols are those wherein all percentages arepercentages by weight:

(1)

85.8% ethyl alcohol

4.3% wood alcohol

4.5% methanol

4.5% isopropyl alcohol

0.9% methylisobutyl ketone;

(2)

89.9% ethyl alcohol

4.5% methanol

4.7% ethyl acetate

0.9% methylisobutyl ketone;

(3)

82.1% ethyl alcohol

17% methanol

0.9% methylisobutyl ketone;

(4)

95.2% ethyl alcohol

1% kerosene

3.8% methylisobutyl ketone.

A wide variety of generally similar denatured ethyl alcohol formulationsmay be employed in the practice of the present invention which do notcause undue depression of the Vicat heat distortion temperature of thepolymer. Up to 25 percent of a denaturing material may be employedprovided that the ethyl alcohol formulation complies with the heatdistortion requirements.

Generally, the preparation of alkenyl aromatic resinous polymer foams inaccordance with the present invention is most conveniently done in amanner generally as shown and described in U.S. Pat. No. 2,669,751,wherein the volatile fluid foaming agent is injected into aheat-plastified polymer stream within an extruder. From the extruder theheat-plastified gel is passed into a mixer, the mixer being a rotarymixer wherein a studded rotor is enclosed within a housing which has astudded internal surface which intermeshes with the studs on the rotor.The heat-plastified gel from the extruder is fed into the inlet end ofthe mixer and discharged from the outlet end, the flow being in agenerally axial direction. From the mixer, the gel passes throughcoolers such as are described in U.S. Pat. No. 2,669,751 and from thecoolers to a die which extrudes a generally rectangular board. Agenerally similar extrusion system and a preferred extrusion system isshown in U.S. Pat. No. 3,966,381.

In the preparation of foams in accordance with the present invention, itis often desirable to add a nucleating agent to reduce the cell size.Talc, calcium silicate, indigo, and the like are suitable agents whichreduce cell size.

Various other additives may be utilized such as fire retardant chemical,stabilizers and the like. A plurality of foams were prepared employing a21/2 inch extruder wherein the foaming agent was admixed with moltenresin, the resin passed to a static cooler, cooled to foamingtemperature and discharged through a slot die having a width of about 3inches. The resultant foam plank had a cross section dimension of about1 inch by 8 inches. In cases where fire retarding agents, stabilizersand/or nucleating agents were added, these were dry blended with theresin pellets prior to entering into the extruder. The results are setforth in the following Table wherein the following abbreviations areemployed:

    ______________________________________                                        Wt %         Weight Percent                                                   PPH          Parts per hundred parts of resin                                 FR agent     Fire retardant agent                                             MGO          Magnesium oxide                                                  DAP          Diammonium hydrogen phosphate                                    BaSt         Barium stearate                                                  TF           Foaming temperature, i.e.,                                                    temperature of resin adjacent                                                 die slot prior to depressure                                                  in degrees centigrade.                                           DIE PRESS.   Die pressure in pounds per                                       (psi)        square inch.                                                     pcf          Pounds per cubic foot                                            mm           Millimeters                                                      V            The vertical direction or                                                     thickness                                                        E            The extrusion direction                                          H            The horizontal or width                                          MeCl         Methyl chloride                                                  F-12         Dichlorodifluoromethane                                          IPA          Isopropyl alcohol                                                ETH          Ethyl alcohol                                                    F-22         Chlorodifluoromethane                                            MeOH         Methyl alcohol                                                   Board        Board when emerging from the                                     formability  forming plate assembly; excellent,                                            meaning relatively smooth skins                                               without roughness; good, meaning                                              some roughness, tolerable for most                                            applications; fair, too rough for                                             many applications.                                               ______________________________________                                    

                                      TABLE                                       __________________________________________________________________________    Effect of Blowing Agent Compositions on Dimensional Stability and Board       Formability                                                                                              Stabilizer                                         Sample                                                                            Blowing Agent F.R. Agent                                                                             (PPH) BaSt                                                                              Indigo                                                                            Talc                                                                              TF                               ID  Type (wt %)                                                                              PPH                                                                              Type  PPH                                                                              MgO                                                                              DAP                                                                              (PPH)                                                                             (PPH)                                                                             (PPH)                                                                             (°C.)                     __________________________________________________________________________    1   50 MeCl/50 F-12                                                                          12.0                                                                             HBCD   1.85                                                                            0.03                                                                             --  0.075                                                                             0.035                                                                            --  123                                  (Control)                                                                 2   20 IPA/80 F-12                                                                           12.0                                                                             HBCD   1.85                                                                            0.03                                                                             -- 0.07                                                                               0.015                                                                            --  128                              3   20 EtOH/80 F-12                                                                          10.6                                                                             --    -- -- -- 0.07                                                                              --  0.2 130                              4   20 EtOH/80 F-12                                                                          12.0                                                                             HBCD   1.80                                                                            0.03                                                                             -- 0.07                                                                              --  0.4 127                              5   20 EtOH/80 F-12                                                                          14.3                                                                             --    -- -- -- 0.07                                                                              --  0.2 130                              6   30 EtOH/70 F-12                                                                          13.0                                                                             --    -- -- -- 0.07                                                                              --  0.4 131                              7   40 EtOH/60 F-12                                                                           8.8                                                                             --    -- -- -- 0.07                                                                              --  0.4 132                              8   50 EtOH/50 F-12                                                                          10.2                                                                             --    -- 0.38                                                                             -- 0.07                                                                              --  0.2 128                              9   13 EtOH/35 F-22/-                                                                        11.5                                                                             --    -- -- --  0.075                                                                            --  --  130                                  52 F-12                                                                   10  16 EtOH/35 F-22/-                                                                        14.3                                                                             --    -- -- --  0.075                                                                            --  --  125                                  49 F-12                                                                   11  23 EtOH/23 F-22/-                                                                        12.0                                                                             --    -- -- --  0.075                                                                            --  --  128                                  54 F-12                                                                   12  26 EtOH/30 F-22/-                                                                        13.5                                                                             --    -- -- --  0.075                                                                            --  --  117                                  44 F-12                                                                   13  50 F-22/50 F-12                                                                          12.0                                                                             --    -- -- --  0.075                                                                            --  --  131                              14  23 EtOH/23 F-22/-                                                                        13.4                                                                             FR-651P                                                                             1.8                                                                              -- 0.5                                                                              0.07                                                                              --  --  119                                  54 F-12                                                                   15  23 EtOH/23 F-22/-                                                                        13.3                                                                             FR-651P                                                                             1.8                                                                              -- 0.5                                                                              0.07                                                                              0.01                                                                              --  116                                  54 F-12                                                                   16  23 EtOH/23 F-22/-                                                                        13.0                                                                             FR-651P                                                                             1.8                                                                              -- 0.8                                                                               0.075                                                                            0.1*                                                                              --  118                                  54 F-12                                                                   17  23 MeOH/23 F-22/-                                                                        12.5                                                                             HBCD  1.8                                                                              --  0.25                                                                            0.15                                                                              0.1*                                                                               0.075                                                                            118                                  54 F-12                                                                   18  8 EtOH/23 MeOH/-                                                                         13.3                                                                             HBCD  1.8                                                                              -- 0.2                                                                              0.15                                                                              0.1*                                                                              0.1 118                                  54 F-12/15 F-22                                                           19  23 EtOH/23 F-22/-                                                                        14.0                                                                             HBCD  1.8                                                                              -- 0.2                                                                              0.15                                                                              0.1*                                                                               0.03                                                                             123                                  54 F-12                                                                   __________________________________________________________________________                                 Dimensional                                                                   Stability at                                                                  1 day** HHI-524C                                     DIE       Cell                                                                              Compressive Strength                                                                     at 158° F., 95% RH,                       Sample                                                                            PRESS.                                                                             Density                                                                            Size                                                                              at 1 day (psi)                                                                           7 days exposure (%)                                                                        Board                               ID  (psi)                                                                              (pcf)                                                                              (mm)                                                                              V   E  H   V   E   H    Formability                         __________________________________________________________________________    1   760  2.02 0.37                                                                              44.2                                                                              20.2                                                                             17.2                                                                              -1.1                                                                              -0.2                                                                              -0.3 Excellent                           2   740  2.98 0.45                                                                              22.8                                                                              32.0                                                                             27.4                                                                              +1.6                                                                              -0.5                                                                              +0.2***                                                                            Fair                                                             +5.7                                                                              +0.2                                                                              +1.4                                     3   660  2.44 0.51                                                                              15.7                                                                              29.0                                                                             21.3                                                                              +1.49                                                                             -0.58                                                                             -0.06                                                                              Good                                4   630  2.23 0.44                                                                              18.1                                                                              34.2                                                                             20.6                                                                              +1.67                                                                             -0.86                                                                             -0.24                                                                              Good                                5   685  1.78 0.54                                                                              14.9                                                                              11.8                                                                              8.4                                                                              +1.52                                                                             -0.01                                                                             +0.67                                                                              Good                                6   790  2.05 0.51                                                                              17.1                                                                              21.0                                                                             15.7                                                                              +1.39                                                                             -0.35                                                                             -0.14                                                                              Good                                7   780  2.61 0.53                                                                              20.1                                                                              29.9                                                                             22.5                                                                              -0.13                                                                             -0.62                                                                             -0.28                                                                              Good                                8   630  2.32 0.55                                                                              11.4                                                                              20.8                                                                             16.9                                                                              +0.7                                                                              +1.6                                                                              +0.6***                                                                            Good                                                             +2.64                                                                             -0.86                                                                             -0.39                                    9   815  2.17 1.01                                                                              19.6                                                                              27.6                                                                             23.4                                                                              +1.2                                                                               0  +0.5 Excellent                           10  725  1.93 1.26                                                                              18.5                                                                              17.5                                                                             16.6                                                                              +1.4                                                                              -0.1                                                                              +0.6 Excellent                           11  650  1.88 0.78                                                                              13.9                                                                              18.1                                                                              9.5                                                                              +1.7                                                                              -0.3                                                                              +1.0 Excellent                           12  750  2.15 1.16                                                                              23.2                                                                              18.3                                                                             22.1                                                                              +0.5                                                                              +1.0                                                                              +0.6 Excellent                           13  840  2.19 0.41                                                                              28.7                                                                              27.5                                                                             27.7                                                                              +0.7                                                                              +0.5                                                                              +0.6 Excellent                           14  800  2.05 0.25                                                                              31.3                                                                              20.1                                                                             19.1                                                                              +0.4                                                                              +0.3                                                                              +0.7 Excellent                           15  700  2.13 0.19                                                                              48.4                                                                              17.5                                                                             18.4                                                                               0  +1.2                                                                              +1.1 Excellent                           16  560  2.02 0.28                                                                              37.0                                                                              11.3                                                                             15.7                                                                              +1.5                                                                              +2.0                                                                              +0.1 Excellent                           17  630  2.11 0.68                                                                              28.4                                                                              21.0                                                                             22.3                                                                              +0.3                                                                              +0.2                                                                              -0.2 Excellent                           18  575  2.27 0.65                                                                              29.9                                                                              26.0                                                                             23.2                                                                              +0.1                                                                              -0.2                                                                              -1.1 Excellent                           19  675  1.77 0.48                                                                              30.5                                                                              9.6                                                                              11.8                                                                              +1.7                                                                              +1.7                                                                              +0.5 Excellent                           __________________________________________________________________________     Note: Samples 3-16 were produced with Ethanol denatured with 9%               isopropanol, 4.3% MeOH, 0.9% MIBK and samples 18 and 19 were produced wit     ethanol denatured with 11.7% methanol and 0.8% MIBK.                          *Phthalocyanine blue pigment instead of indigo.                               DAP = diammonium hydrogen phosphate.                                          **This federal specification for insulation products requires dimensional     changes not more than ±2.0% in any direction at 158° F./95%         relative humidity for 7 days exposure.                                        ***22 hours at 167° F. one day after production.                  

                              Stabilizer     Roman                                Sample                                                                            Blowing Agent F.R. Agent                                                                            (PPH)  BaST                                                                              Indigo                                                                            Blue*                                                                             TF                               ID  Type (wt %)                                                                             PPH Type PPH                                                                              MgO                                                                              DAP (PPH)                                                                             (PPH)                                                                             (PPH)                                                                             (°C.)                     __________________________________________________________________________    20  23 EtOH/23 F-22/-                                                                       12.0                                                                              FR-651P                                                                            1.0                                                                              0.03                                                                             --  0.07                                                                              0.01                                                                              --  125                                  54 F-12                                                                   21  23 EtOH/23 F-22/-                                                                       12.0                                                                              FR-651P                                                                            1.0                                                                              -- 0.25                                                                              0.07                                                                              --  0.01                                                                              123                                  54 F-12                                                                   22  23 EtOH/23 F-22/-                                                                       12.0                                                                              HBCD 1.0                                                                              -- 0.25                                                                              0.07                                                                              0.01                                                                              --  128                                  54 F-12                                                                   23  23 EtOH/23 F-22/-                                                                       12.0                                                                              HBCD 1.0                                                                              0.05                                                                             --  0.07                                                                              0.01                                                                              --  128                                  54 F-12                                                                   24  23 EtOH/23 F-22/-                                                                       12.0                                                                              HBCD 1.0                                                                              -- 0.25                                                                              0.07                                                                              --  0.01                                                                              125                                  54 F-12                                                                   __________________________________________________________________________                                  Dimensional Stability                                                     Cell                                                                              at 1 day (%)** 167° F./                                   Sample                                                                            Density                                                                            Size                                                                              22 hour exposure                                                                          Board                                                ID  (pcf)                                                                              (mm)                                                                              V   E   H   Formability                         __________________________________________________________________________                     20  2.06 0.30                                                                              +0.09                                                                             -0.91                                                                             -0.17                                                                             Excellent                                            21  1.97 0.32                                                                              -0.74                                                                             -0.53                                                                             -0.88                                                                             Excellent                                            22  1.92 0.75                                                                              +1.54                                                                             -0.64                                                                             -0.97                                                                             Excellent                                            23  1.92 0.58                                                                              +0.46                                                                             -0.74                                                                             -0.60                                                                             Excellent                                            24  2.0  0.61                                                                              +0.75                                                                             -0.52                                                                             -0.96                                                                             Excellent                           __________________________________________________________________________     Note:                                                                         *Roma Blue = phthalocyanine blue pigment.                                     Die pressure = 600-700 psi.                                                   Samples 20-24 were produced with ethanol denatured with 11.7% methanol an     0.8% MIBK.                                                                    **Criteria for dimensional stability requires dimensional change less tha     2% in any direction.                                                     

Foams in accordance with the present invention shown excellent retentionof thermal insulating properties, with time, due to the presence of thechlorofluoromethane as well as providing desirable dimensionalstability. The dimensional stability was determined by heating foam for22 hours at 75 degrees centigrade.

In a manner similar to the foregoing a wide variety of lower alcoholcontaining fluorocarbon mixtures are readily employed to form desirablealkenyl aromatic resinous foams.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in thehereto-appended claims.

What is claimed is:
 1. A synthetic resinous thermoplastic foam preparedin accordance with the hereinbefore described method wherein an alkenylaromatic thermoplastic synthetic resinous elongate foam body having amachine direction and a transverse direction, the body defining aplurality of closed noninterconnecting gas-containing cells therein, thecells having an average cell size of from about 0.1 to 1.2 millimeters,the foam body being of a generally uniform cellular structure and beingwithout discontinuities, the body being without substantial variation inaverage cell size when cell size is measured by averaging cell diameteracross the minimum cross-sectional dimension of the body (i.e., such asby ASTM Method D2842-69), the elongate body having a cross-sectionalarea of at least 8 square inches and having a minimum cross-sectionaldimension of at least 0.25 inch, the foam body having a water vaporpermeability not greater than 1.8 perm inches as measured by ASTM MethodC355-64 Procedures for Desiccant method, a density of from about 1 toabout 5 pounds per cubic foot with the further limitation that the cellscontain a blowing agent which has a permeability through the alkenylaromatic resinous polymer of not greater than 0.017 times thepermeability of nitrogen through the body, a C₁ to C₃ monohydric alcoholand the blowing agent having a thermal conductivity of 0.08 Britishthermal units-inch per hour per square foot per degree Fahrenheit,wherein the foam is prepared by extrusion employing a blowing agentselected from the group consisting of(1) a mixture of from about 5 to 20weight percent isopropyl alcohol, from about 5 to 50 percentchlorodifluoromethane, and from about 30 to 70 percentdichlorodifluoromethane; (2) a mixture of from about 5 to 50 percent ofan ethanol, methanol or mixtures thereof, from about 5 to 50 percent ofchlorodifluoromethane, and about 30 to 70 percentdichlorodifluoromethane; and mixtures thereof, all percentages being byweight.